The present invention relates, in general, to the measurement of vorticity in a flowing fluid, and more particularly to the use of minute reflectors within the liquid which will rotate with the fluid, and optical and circuit means for measuring the rotation of such reflectors.
Although the vorticity field, .omega.(x,t)=.gradient.x v(x,t), is an essential property of rotational and tubulent flow, the measurement of vorticity exceeds present experimental capability. Present techniques of hot wire and film anemometry and laser doppler anemometry can measure components of the velocity field v(x,t) at a limited number of points, and the velocity components are ordinarily analyzed by finite differences or by the application of Taylor's frozen flow hypothesis to calculate the vorticity, but error magnification by the necessary differentiations limits the accuracy and spectral range. Spatial resolution has usually been limited to about 0.1 cm by hot probe geometry; recent experimenters have improved the spatial resolution to 100 .mu.m. In principle, flow perturbations can be avoided and the spatial resolution can be slightly improved by laser doppler anemometry but the complexity of these simultaneous optical measurements has apparently deterred its application to vorticity measurement.